"For Buddhists everywhere, the Bhavacakra is a powerful reminder of samsara, the cycles of transmigratory existence that operate both physically and psychologically in the lives of all beings. At its hub the three poisons, a pig, cock, and snake—symbols of ignorance, greed, and hatred—chase each other endlessly, binding beings to the cycle of suffering through the power of karma.
The six divisions in the spokes of the wheel depict the six realms in which living beings take birth. Uppermost are the heavenly realms of the devas, or gods. To the left and right are the realms of humans and asuras, powerful beings ruled by anger and jealousy. The lower divisions contain the animal realm, the desolate fields of the hungry ghosts, and the burning and freezing hells.
Forming the rim of the wheel are twelve images depicting the twelve links of pratitya samutpada, or interdependent origination. Beginning with ignorance and ending with birth, old age, and death, each link in the chain becomes the cause of the next, perpetuating ceaseless cycles of cause and result. Magnetized by the flow of events, beings are cast down from the heavens to the hells and flung into the intermediate realms according to their karma and the conjunction of causes and conditions.
Holding the wheel firmly in his grasp is Yama, lord of death, the end of all living beings, even the gods. A Buddha, or Tathagata, stands outside the wheel, demonstrating the possibility of liberation." ~Tarthang Rinpoche, Dharma Publishing